Pressure balancing accumulator

ABSTRACT

An accumulator and associated method substantially reduces if not eliminates a bump energy event associated with the use of a U-tube. A bypass or pressure equalizing passage is provided between upper portions of a U-shape return tube for reducing the pressure difference on opposite sides of any accumulated liquid refrigerant in the bottom of the U-tube upon compressor start-up. This prevents or substantially prevents the liquid “slug” from entering the suction line leading to the compressor. The diameter of the U-tube in the lower region of the accumulator&#39;s canister is reduced relative to the diameter of the upper portions of the return tube, thereby reducing the volume of liquid refrigerant that can accumulate in the return tube. The reduction also increases the flow velocity of the gas phase refrigerant for improving oil recirculation.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/793,213 filed Apr. 19, 2006 and 60/802,441 filed May 22, 2006, both of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The herein described invention relates generally to accumulators for air conditioner and other refrigerant systems and the like, including in particular accumulators using U-shaped or J-shaped tubes and particular.

BACKGROUND OF THE INVENTION

Conventional refrigeration systems include a compressor, a condenser, an expansion device, and an evaporator. Refrigerant is circulated through the system to produce cooling. Energy is provided to the system by the compressor which serves to create a source of high pressure gas refrigerant that is allowed to pass through the condenser. The refrigerant dissipates heat in the condenser and changes state to a high pressure liquid. The refrigerant then passes through the expansion device and into the evaporator where the refrigerant changes state from a high pressure liquid to a low pressure liquid, and subsequently to a low pressure gas. The change of state removes heat from the area surrounding the evaporator. The refrigerant is then drawn from the evaporator back to the compressor in a low pressure gas form, where it is again compressed into high pressure gas for repetition of the cycle.

An accumulator is also normally located between the evaporator and the compressor in the refrigeration system. The accumulator ensures that only refrigerant in a vapor stage passes on to the compressor, as refrigerant from the outlet of the evaporator typically includes both a liquid component and a vapor component. Some accumulators employ a U-shaped or J-shaped return conduit in a canister. The outlet end of the return conduit is connected to the suction line leading to the compressor, and the inlet end of the return conduit opens to the upper region of the canister where the vapor component is collected. The liquid component of the stream flowing into the accumulator, along with any lubricating oil, will drain to the lower region of the canister. The return conduit typically includes a metering device at its lower end that draws a small amount of oil in the liquid refrigerant back into the return tube for lubrication of the downstream components, e.g. the compressor.

During times when the compressor is not running, liquid refrigerant accumulates in the bottom of the canister. This accumulated liquid can migrate through the oil return orifice in the return tube, and the liquid level in the return tube can equal the liquid level in the canister. When the compressor restarts, a substantial pressure drop occurs in the return line and the liquid in the bottom of the return tube can be drawn into the suction line while violently boiling into a vapor. This event is commonly referred to as accumulator “thump” or “bump”.

Attempts have been made to eliminate the bump energy by removing the U-shaped or J-shaped tube from the accumulator. One such attempt described in U.S. Pat. No. 6,418,751 uses a trumpet-style vapor inlet with a venturi portion to create refrigeration velocity for oil return pickup. Although this design does reduce the bump energy, it has difficulty returning a sufficient amount of oil back to the compressor. Another attempt disclosed in U.S. Pat. No. 6,389,842 provides adequate oil recirculation, but does not adequately eliminate the bump energy event.

SUMMARY OF THE INVENTION

The present invention provides an accumulator and associated method for substantially reducing if not eliminating the bump energy event. According to one aspect of the invention, a bypass or pressure equalizing passage is provided between upper portions of a U-shape return tube for reducing the pressure difference on opposite sides of any accumulated liquid refrigerant in the bottom of the return tube upon compressor start-up. This prevents or substantially prevents the liquid “slug” from entering the suction line leading to the compressor. The reduced pressure difference also reduces the rate of “boiling” of the liquid resulting from the sudden drop of pressure at the accumulator outlet.

According to another aspect of the invention, the diameter of the U-shape return tube in the lower region of the accumulator's canister is reduced relative to the diameter of the upper portions of the return tube, thereby reducing the volume of liquid refrigerant that can accumulate in the return tube. The reduction also increases the flow velocity of the gas phase refrigerant for improving oil recirculation. The inside diameter of the bottom of the return tube can be approximately the same as a tube connecting the upper ends of the return tube. In addition, the combined cross-sectional areas of the connecting tube and lower region of the U-tube can be approximately equal the flow area of the upper ends of the return tube.

Accordingly, an accumulator for a refrigerant that circulates in a closed-loop refrigeration system, comprises a closed container having an inlet for receiving refrigerant in mixed liquid/gas phase from an evaporator such that the gas phase will accumulate in an upper region of the container and refrigerant in the liquid phase will accumulate in a lower region of the container. A return conduit in said container has an inlet portion, an outlet portion, and a lower U-shape portion connecting the inlet portion to the outlet portion. The inlet portion has an inlet end opening to the upper region of the container for drawing gas phase refrigerant into the return conduit, the outlet portion terminates at an outlet connectable to a suction line leading to a compressor of the closed-loop system, and the U-shape portion has a metering device communicating with the lower region of the container for drawing lubricant bearing liquid refrigerant into the return conduit so as to be entrained in the gas phase refrigerant flowing therethrough for lubrication of the compressor. In accordance with the invention, a bypass passage is provided for supplying gas phase refrigerant from the upper region of the container to the outlet portion without passage through the U-shape portion, whereby suction at the outlet of the outlet portion draws gas phase refrigerant through both the U-shape portion and the bypass passage.

The U-shape portion may have a minimum cross-sectional area less than the minimum cross-sectional area of the outlet portion adjacent but downstream of the bypass passage. The U-shape portion may have a minimum cross-sectional area less than the minimum cross-sectional area of the inlet portion.

In a preferred embodiment, the U-shape portion over the length thereof has a reduced cross-sectional area less than the cross-sectional areas of the outlet and inlet portions, whereby the volume of liquid phase refrigerant that may migrate into the U-shape portion through the metering device and assume the level of liquid phase refrigerant in the container will be less than the volume if the U-shape portion had the same cross-sectional areas as the outlet and inlet portions.

In one embodiment, the bypass passage is formed by a connection tube connected between the outlet portion of the return conduit and the inlet portion of the return conduit at a location above the U-shape portion, whereby the connection tube communicates with the upper region of the container via the inlet portion of the return conduit. The inlet portion may have a minimum cross-sectional area at least equal the combined minimum cross-sectional areas of the bypass passage and U-shape portion. The connection tube may be substantially perpendicular to one or both of the inlet and outlet portions of the return conduit.

In another embodiment, the bypass passage is formed by a bypass inlet tube connected at a downstream end to the outlet portion of the return conduit and having an upstream end opening to the upper region of the container.

In yet another embodiment, the return conduit is formed by a tube, and the bypass passage is formed by a hole in a wall of the outlet portion of the tube, which hole is located in the upper region of the container.

The container may have a top wall, and the outlet portion of the return conduit may exit the container through the top wall of the container.

The various conduits or portions thereof may be formed by a tube or tubes made of a suitable material such as aluminum or plastic compatible with the refrigerant.

According to another aspect of the invention, an accumulator for a refrigerant that circulates in a closed-loop refrigeration system, comprises a closed container having an inlet for receiving refrigerant in mixed liquid/gas phase from an evaporator such that gas phase refrigerant will accumulate in an upper region of the container and liquid phase refrigerant will accumulate in a lower region of the container; an outlet connectable to a suction line leading to a compressor of the closed-loop system; and a dual flow conduit assembly connected to the outlet for drawing to the outlet gas phase refrigerant from the upper region of the container along first and second conduits. The first conduit has a U-shape portion having a metering device communicating with the lower region of the container for drawing lubricant bearing liquid refrigerant into the first conduit so as to be entrained in the gas phase refrigerant passing therethrough for lubrication of the compressor.

The U-shape portion preferably has along the length thereof a reduced cross-sectional area less than the cross-sectional area of the outlet to which the first and second flow paths connect. The U-shape portion may extend between a vertical inlet portion of the first conduit and a vertical outlet portion of the first conduit. The second conduit may have a vertical inlet portion opening to the upper region of the container, a horizontal outlet portion, and a curved portion extending between the vertical inlet and horizontal outlet portions of the second conduit. The U-shape portion may extend between a vertical inlet portion of the first conduit and a vertical outlet portion of the first conduit. The vertical outlet portion of the first conduit may be connected to the horizontal outlet portion of the second conduit.

The horizontal outlet portion preferably is located in the upper region of the container and has at an underside thereof a drain opening for allowing any accumulated liquid phase refrigerant to drain out of the horizontal portion of the second conduit. The second conduit may also have a U-shape portion with the bottom thereof located at a higher level in the container than the bottom of the U-shape portion of the first conduit, and the U-shape portion may have at the bottom thereof a drain opening for allowing any accumulated liquid phase refrigerant to drain out of the horizontal portion of the second conduit.

The invention also provides a method for separating liquid phase refrigerant from a mixed liquid/gas phase refrigerant flowing from an evaporator in a closed-loop refrigeration system, comprising the steps of directing the mixed liquid/gas phase refrigerant into a container that has an outlet connected to a compressor of the refrigeration system, and using a dual flow conduit assembly connected to the outlet for drawing to the outlet gas phase refrigerant from the upper region of the container along first and second conduits, wherein the first conduit has a U-shape portion having a metering device communicating with the lower region of the container for drawing lubricant bearing liquid refrigerant into the first conduit so as to be entrained in the gas phase refrigerant passing therethrough for lubrication of the compressor.

Further features of the invention will become apparent from the following detailed description when considered in conjunction with the drawings.

BRIEF DESCRIPTION OF DRAWINGS

In the annexed drawings:

FIG. 1 is a cross-sectional view of an exemplary accumulator according to the present invention;

FIG. 2 is a cross-sectional view of the accumulator of FIG. 1, taken at right angles to the view of FIG. 1;

FIGS. 3-7 are cross-sectional views of other exemplary accumulators according to the present invention; and

FIG. 8 is a perspective view of another return conduit assembly of an accumulator according to the invention.

DETAILED DESCRIPTION

Referring now to the drawings in detail and initially to FIGS. 1 and 2, an exemplary accumulator according to the principles of the present invention is illustrated generally at 20. The accumulator includes an outer canister, housing or other container 22. The container 22 has a tubular sidewall or shell 24, an upper end wall 26 and a lower end wall 28. The shell may be cylindrical, and the sidewall and lower end wall may be formed together in one piece using common forming techniques such as impacting or extruding a sheet of metal or injection molding plastic. The upper end wall 26 may be formed separately as a cap or cover that is joined by any suitable means in a fluid-tight manner to the upper end of the shell 24. The upper end wall 26, lower end wall 28 and cylindrical sidewall 24 define an internal chamber indicated generally by reference number 30. As shown, the end walls may be convexly or dome shaped as is conventional.

The illustrated accumulator 20 is particularly suited for incorporation in refrigeration system such as an automotive air-conditioning system, typically between the outlet side of an evaporator and the inlet side of a compressor. As known to those skilled in the art, the accumulator is generally designed to store excess liquid in the refrigeration system, and pass vaporous or gaseous refrigerant to the compressor. Liquid phase refrigerant will accumulate in the lower region of the accumulator.

The accumulator 20 includes an inlet 34 for directing refrigerant in a liquid and vapor (or gas) state into chamber 30, and a return conduit assembly 36 extending from within the chamber 30 to an outlet 38 for directing gas phase refrigerant from an upper region of the chamber out of chamber 30 for passage to the downstream compressor. The inlet 34 may be formed by a tube 40 formed as one piece with the cover 26 or attached to the cover, although it will be appreciated that the inlet may be otherwise formed and/or located. The upper region of the container may also be provided with baffles or other flow directing structures (not shown) as is known in the art to facilitate separation of liquid phase refrigerant from gas phase refrigerant to be passed on to the compressor via the return conduit assembly. The outlet 38 may also be formed by a tube 42 that preferably protrudes from the cover or other wall of the container. Appropriate fittings (not shown) may be provided for the inlet and outlet tubes such that the accumulator can be connected to refrigerant flow lines in the refrigeration system.

The return conduit assembly 36 in the container 20 has a vertically extending inlet portion 46, a vertically extending outlet portion 48, and a lower U-shape portion 50 connecting the inlet portion to the outlet portion. The inlet portion has an inlet end 52 opening to the upper region of the chamber 30 in the container for drawing gas phase refrigerant into the return conduit. The outlet portion terminates at the outlet tube 42 that may simply be an extension of the outlet portion of the return conduit assembly.

The U-shape portion 50 has a metering device 56 at the lower end thereof that resides in a lower region of the container 22. The metering device 56 may be of any suitable type providing for metered flow of lubricant bearing liquid refrigerant stored in the lower region of the container into the U-shape portion 50 so as to be entrained in the gas phase refrigerant flowing through U-shape portion for lubrication of the compressor or other system components downstream of the accumulator. As is well known, a lubrication oil is commonly added to the refrigerant for lubricating purposes. It is contemplated that a refrigerant may itself have some lubricating properties so as to negate the need to add a lubricating oil. The term lubricant bearing refrigerant is intended to encompass either situation, i.e. a refrigerant to which a lubricant has been added or a refrigerant with inherent lubricating properties.

In the illustrated embodiment, the metering device 56 is a bleed orifice although as noted any other devices may be used that meter a controlled amount of oil in the stored refrigerant (as well as a controlled amount of liquid refrigerant) into the return conduit for return to the compressor. The bleed orifice may be provided with a filter to prevent the orifice from clogging, as is known in the art.

The various portions of the return conduit assembly 36 may be formed by tubes or portions of a common tube as the case may be. The return conduit assembly may be mounted in the container in any suitable manner, such as by the connection of the tubes to the cover or walls of the container. The bottom of the return conduit assembly may be provided with a gusset for resting on the bottom end wall of the container for improved stability and support, and various brackets or gussets may also be employed as desired. The tube or tubes may be made of a suitable material such as aluminum or plastic compatible with the refrigerant.

In accordance with the invention, a bypass passage 60 is provided for supplying gas phase refrigerant from the upper region of the container 22 to the outlet 38 without passage through the U-shape portion 50, whereby suction at the outlet of the outlet portion draws gas phase refrigerant through both the U-shape portion and the bypass passage 60. The bypass passage may take various configurations, including those exemplified herein. As will be appreciated, the bypass passage and U-shape portion provide respective flow paths or conduits for gas phase refrigerant, with one path being through the U-shape portion that extends into the lower region of the container for picking up lubricant bearing liquid refrigerant. As noted above, the bypass, or pressure equalizing, passage is provided between upper portions of a U-shape portion for reducing the pressure difference on opposite sides of any accumulated liquid refrigerant in the bottom of the return tube upon compressor start-up. During times when the compressor is not running, liquid refrigerant accumulates in the bottom of the canister. This accumulated liquid can migrate through the oil return orifice in the return tube, and the liquid level in the return tube can equal the liquid level in the canister. When the compressor restarts, a substantial pressure drop occurs in the return line and the liquid in the bottom of the return tube can be drawn into the suction line while violently boiling into a vapor. This event is commonly referred to as accumulator “thump” or “bump”. The bypass or pressure equalizing passage prevents or substantially prevents the liquid “slug” from entering the suction line leading to the compressor. The reduced pressure difference across the U-shape portion also reduces the rate of “boiling” of the liquid slug resulting from the sudden drop of pressure at the accumulator outlet.

In the exemplary accumulator shown in FIGS. 1 and 2, the bypass passage 60 is formed by a connection tube 66 connected between the outlet portion 48 of the return conduit and the inlet portion 46 of the return conduit at a location above the U-shape portion 50, whereby the connection tube communicates with the upper region of the container via the inlet portion of the return conduit. The inlet portion may have a minimum inside cross-sectional area at least equal the combined minimum inside cross-sectional areas of the bypass tube 66 and U-shape portion (or U-tube). The connection tube may be substantially perpendicular to one or both of the inlet and outlet portions of the return conduit.

According to another aspect of the invention, the inside diameter of the U-shape portion or tube 50 in the lower region of the accumulator's canister is reduced relative to the inside diameter of upper portions 46 and 48 of the return tube, in particular the outlet portion of the return tube connected to the outlet tube. This reduces the volume of liquid refrigerant that can accumulate in the return tube. The reduction also increases the flow velocity of the gas phase refrigerant for improving oil recirculation.

The inside diameter of the bottom of the return tube can be approximately the same as the connecting tube connecting the upper ends of the return tube. In addition, the combined cross-sectional areas of the connecting tube and lower region of the U-tube can be approximately equal the flow area of the upper ends of the return tube.

The U-shape portion 50 may have a minimum inside cross-sectional area less than the minimum inside cross-sectional area of the outlet portion 46 adjacent but downstream of the bypass passage 60. The U-shape portion may have a minimum inside cross-sectional area less than the minimum inside cross-sectional area of the inlet portion.

In a preferred embodiment, the U-shape portion or tube 50 over the length thereof has a reduced inside cross-sectional area less than the inside cross-sectional areas of the outlet and/or inlet tube portions 46 and 48. Preferably this diameter extends over the portion of the U-tube that will be submerged in liquid refrigerant accumulated in the lower region of the container 28. That is, the accumulator and refrigerant volume may be designed for a maximum accumulation design level in the container, and the reduced diameter portion of the U-tube extends to a height above the design level, thereby to minimize the volume of the refrigerant slug under anticipated operating conditions. Although less desirable, another embodiment may provide the reduced diameter only over a relatively small portion of the U-tube, such as a portion of the bottom of the U-tube containing the metering orifice. As illustrated in the several drawings, transitions between different diameter sections of tubes can be made by tapered sections that provide for a progressive, rather than an abrupt, transition.

Another exemplary accumulator is shown in FIG. 3, wherein parts and features corresponding to similar parts and features of the accumulator of FIGS. 1 and 2 are designated by the same reference numeral incremented by 100. In the accumulator 120, the bypass passage 160 is formed by a bypass inlet tube 161 connected at a downstream end to the outlet portion 148 of the return conduit 136 and having an upstream end 163 opening to the upper region of the container 122. In this embodiment, the reduced diameter of the U-shape tube 150 can be carried all the up through the inlet portion 146 of the return tube as shown.

A further exemplary accumulator is shown in FIG. 4, wherein parts and features corresponding to similar parts and features of the accumulator of FIGS. 1 and 2 are designated by the same reference numeral incremented by 200. In the accumulator 220, the bypass passage 260 is formed by a hole 267 in the wall of the outlet portion 248 of the return tube 236, which hole is located in the upper region of the container 222 and downstream of the U-shape tube portion 252. Again, the reduced diameter of the U-shape tube can be carried all the up through the inlet portion of the return tube as shown.

Still another exemplary accumulator is illustrated in FIG. 5, wherein parts and features corresponding to similar parts and features of the accumulator of FIGS. 1 and 2 are designated by the same reference numeral incremented by 300. The accumulator 320 operates somewhat differently from the embodiments of FIGS. 1-4, but shares therewith the principle of providing a dual flow return conduit assembly 336 having two flow paths or conduits 337 and 339 connected to the outlet 338 for drawing to the outlet gas phase refrigerant from the upper region of the container 322 along the first and second conduits, with one 339 of the flow paths or conduits having a U-shape portion 350 with a metering device 356 communicating with the lower region of the container for drawing lubricant bearing liquid refrigerant into the U-shape portion 350 so as to be entrained in the gas phase refrigerant passing therethrough for lubrication of the compressor.

As shown in FIG. 5, the other conduit 337 may have a vertical inlet portion 341 opening to the upper region of the container, a horizontal outlet portion 343, and a curved portion 345 extending between the vertical inlet and horizontal outlet portions of the second conduit. The U-shape portion may extend between a vertical inlet portion 361 and a vertical outlet portion 363. The vertical outlet portion 363 may be connected to the horizontal outlet portion 343.

The horizontal outlet portion 343 preferably is located in the upper region of the container and has at an underside thereof a drain opening 371 for allowing any accumulated liquid phase refrigerant to drain out of the horizontal portion before passage to the U-shape portion 350.

An accumulator similar in function to the FIG. 5 design is shown in FIG. 6, wherein parts and features corresponding to similar parts and features of the accumulator of FIG. 5 are designated by the same reference numeral incremented by 100. In the accumulator 420, the second conduit or tube 437 may also have a U-shape portion 411 with the bottom thereof located at a higher level in the container than the bottom of the U-shape portion of the first conduit. This U-shape portion may have at the bottom thereof a drain opening 413 for allowing any accumulated liquid phase refrigerant to drain out of the horizontal portion of the second conduit.

Another accumulator 520 similar to the accumulator 420 shown in FIG. 6 is shown in FIG. 7, wherein parts and features corresponding to similar parts and features of the accumulator of FIG. 6 are designated by the same reference numeral incremented by 100. In the accumulator 520, the upper inlet ends of the U-shape conduits or tubes open in parallel relationship to a common inlet tube 523 of larger inside diameter, and the upper ends of the U-shape conduits or tubes open in parallel relationship to a common outlet tube 525 of larger inside diameter.

FIG. 8 shows another exemplary return conduit assembly 636 similar to the accumulator 20 of FIGS. 1 and 2. Again, corresponding parts and features are designated by the same reference number but incremented by 500. The aforementioned strengthening gussets 679 and 681 are illustrated, as is an outlet fitting assembly 683 that provides for attachment of the conduit assembly 636 to the sidewall of the container as well as connection to tubing leading to the compressor. The conduit assembly may be molded from plastic. The collar 685 and tubular insert 687 are shown in exploded view, but will be molded in the tubular outlet 689 of the conduit assembly. That is, the metal parts will be placed in a mold and then plastic may be injected into the mold such that they will be retained in the molded conduit assembly when it is removed from the mold. The right-hand portion of the tubular insert will be axially coextensive with both the end portion 691 of the tubular outlet and the collar. Thus, the end portion of the tubular outlet will be sandwiched between the collar and insert. The collar and insert may have on the surfaces thereof that contact the plastic end portion recesses to provide a mechanical interlock with the plastic part as desired. The assembly may then be installed into a container with the projecting portion of the insert inserted through a hole in the sidewall of the container. Then a metal tube fitting 693 can be assembled over the insert projecting from the sidewall and the two parts secured together as by crimping. The insert, for example, the insert may be radially expanded into the collar portion 695 of the tube fitting, which collar portion may be grooved on its inner diameter to provide a mechanical lock with the insert. The sidewall of the container will be tightly trapped between the collar and the tube fitting, thereby holding the conduit assembly in place in the container. Suitable seals may be provided as desired. The balance of the tube fitting provides for coupling with a suction tube.

As should be apparent from the above, an accumulator according to the invention can be relatively easy to manufacture and assemble.

Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application. 

1. An accumulator for a refrigerant that circulates in a closed-loop refrigeration system, comprising a closed container having an inlet for receiving refrigerant in mixed liquid/gas phase from an evaporator such that the gas phase will accumulate in an upper region of the container and refrigerant in the liquid phase will accumulate in a lower region of the container; a return conduit in said container, said return conduit having an inlet portion, an outlet portion, and a lower U-shape portion connecting the inlet portion to the outlet portion, the inlet portion having an inlet end opening to the upper region of the container for drawing gas phase refrigerant into the return conduit, the outlet portion terminating at an outlet connectable to a suction line leading to a compressor of the closed-loop system, and the U-shape portion having a metering device communicating with the lower region of the container for drawing lubricant bearing liquid refrigerant into the return conduit so as to be entrained in the gas phase refrigerant flowing therethrough for lubrication of the compressor; and a bypass passage for supplying gas phase refrigerant from the upper region of the container to the outlet portion without passage through the U-shape portion, whereby suction at the outlet of the outlet portion draws gas phase refrigerant through both the U-shape portion and the bypass passage.
 2. An accumulator according to claim 1, wherein the U-shape portion has a minimum cross-sectional area less than the minimum cross-sectional area of the outlet portion adjacent but downstream of the bypass passage.
 3. An accumulator according to claim 2, wherein the U-shape portion has a minimum cross-sectional area less than the minimum cross-sectional area of the inlet portion.
 4. An accumulator according to claim 1, wherein the U-shape portion over the length thereof has a reduced cross-sectional area less than the cross-sectional areas of the outlet and inlet portions, whereby the volume of liquid phase refrigerant that may migrate into the U-shape portion through the metering device and assume the level of liquid phase refrigerant in the container will be less than the volume if the U-shape portion had the same cross-sectional areas as the outlet and inlet portions.
 5. An accumulator according to claim 1, wherein the return conduit over the portion thereof located in a lower half of the container has a cross-sectional area less than the cross-sectional area of at least one of the inlet and outlet portions located in an upper half of the container.
 6. An accumulator according to claim 1, wherein the bypass passage is formed by a connection tube connected between the outlet portion of the return conduit and the inlet portion of the return conduit at a location above the U-shape portion, whereby the connection tube communicates with the upper region of the container via the inlet portion of the return conduit.
 7. An accumulator according to claim 6, wherein the inlet portion has a minimum cross-sectional area at least equal the combined minimum cross- sectional areas of the bypass passage and U-shape portion.
 8. An accumulator according to claim 6, wherein the connection tube is substantially perpendicular to one or both of the inlet and outlet portions of the return conduit.
 9. An accumulator according to claims 1, wherein the bypass passage is formed by a bypass inlet tube connected at a downstream end to the outlet portion of the return conduit and having an upstream end opening to the upper region of the container.
 10. An accumulator according to claim 1, wherein return conduit is formed by a tube, and the bypass passage is formed by a hole in a wall of the outlet portion of the tube, which hole is located in the upper region of the container.
 11. An accumulator according to claim 1, wherein the container has a top wall, and the outlet portion of the return conduit exits the container through the top wall of the container.
 12. An accumulator according to claim 1, wherein the return conduit is formed by a tube.
 13. An accumulator for a refrigerant that circulates in a closed-loop refrigeration system, comprising a closed container having an inlet for receiving refrigerant in mixed liquid/gas phase from an evaporator such that gas phase refrigerant will accumulate in an upper region of the container and liquid phase refrigerant will accumulate in a lower region of the container; an outlet connectable to a suction line leading to a compressor of the closed- loop system; and a dual flow conduit assembly connected to the outlet for drawing to the outlet gas phase refrigerant from the upper region of the container along first and second conduits, and the first conduit has a U-shape portion having a metering device communicating with the lower region of the container for drawing lubricant bearing liquid refrigerant into the first conduit so as to be entrained in the gas phase refrigerant passing therethrough for lubrication of the compressor.
 14. An accumulator according to claim 13, wherein the U-shape portion has along the length thereof a reduced cross-sectional area less than the cross-sectional area of the outlet to which the first and second flow paths connect.
 15. An accumulator according to claim 13, wherein the U-shape portion extends between a vertical inlet portion of the first conduit and a vertical outlet portion of the first conduit.
 16. An accumulator according to claim 13, wherein the second conduit has a vertical inlet portion opening to the upper region of the container, a horizontal outlet portion, and a curved portion extending between the vertical inlet and horizontal outlet portions of the second conduit.
 17. An accumulator according to claim 16, wherein the U-shape portion extends between a vertical inlet portion of the first conduit and a vertical outlet portion of the first conduit.
 18. An accumulator according to claim 17, wherein the vertical outlet portion of the first conduit is connected to the horizontal outlet portion of the second conduit.
 19. An accumulator according to claim 13, wherein the horizontal outlet portion is located in the upper region of the container and has at an underside thereof a drain opening for allowing any accumulated liquid phase refrigerant to drain out of the horizontal portion of the second conduit.
 20. An accumulator according to claim 13, wherein the second conduit has a U-shape portion with a bottom thereof located at a higher level in the container than a bottom of the U-shape portion of the first conduit, and the U-shape portion has at the bottom thereof a drain opening for allowing any accumulated liquid phase refrigerant to drain out of the horizontal portion of the second conduit.
 21. A method for separating liquid phase refrigerant from a mixed liquid/gas phase refrigerant flowing from an evaporator in a closed-loop refrigeration system, comprising the steps of directing the mixed liquid/gas phase refrigerant into a container that has an outlet connected to a compressor of the refrigeration system, and using a dual flow conduit assembly connected to the outlet for drawing to the outlet gas phase refrigerant from the upper region of the container along first and second conduits, wherein the first conduit has a U-shape portion having a metering device communicating with the lower region of the container for drawing lubricant bearing liquid refrigerant into the first conduit so as to be entrained in the gas phase refrigerant passing therethrough for lubrication of the compressor. 